java Hibernate延迟加载

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示例数据表：team(班级)、certificate(身份证)、student(学生)

Team.hbm.xml
?xml version="1.0" encoding="utf-8"?
!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"
!--
    Mapping file autogenerated by MyEclipse Persistence Tools
--
hibernate-mapping
    class name="edu.dgut.ke.model.Team" table="TEAM" lazy ="true" !-- 多对一的延迟加载设置 --
        id name="id" type="java.lang.String"
            column name="ID" length="32" /
            generator class="uuid.hex" /
        /id
        property name="teamname" type="java.lang.String"
            column name="TEAMNAME" length="32" not-null="true" unique="true" /
        /property
        set name="students" inverse="true" cascade="all" lazy="true" !-- 一对多的延迟加载设置 --
            key
                column name="TEAMID" length="32" not-null="true" /
            /key
            one-to-many class="edu.dgut.ke.model.Student" /
        /set
    /class
/hibernate-mapping

Certificate.hbm.xml
?xml version="1.0" encoding="utf-8"?
!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"
!--
    Mapping file autogenerated by MyEclipse Persistence Tools
--
hibernate-mapping
    class name="edu.dgut.ke.model.Certificate" table="CERTIFICATE" lazy="true" !-- 一对一的延迟加载设置 --

        id name="id" type="java.lang.String"
            column name="ID" length="32" /
            generator class="uuid"

            /generator
        /id
        property name="describe" type="java.lang.String"
            column name="`DESCRIBE`" length="50" not-null="true" /
        /property
        one-to-one name="student"
        class="edu.dgut.ke.model.Student"
         constrained="true" !-- 一对一的延迟加载设置 --

        /one-to-one
    /class
/hibernate-mapping

Student.hbm.xml
?xml version="1.0" encoding="utf-8"?
!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"
!--
    Mapping file autogenerated by MyEclipse Persistence Tools
--
hibernate-mapping
    class name="edu.dgut.ke.model.Student" table="STUDENT" lazy="true"
        id name="id" type="java.lang.String"
            column name="ID" length="32" /
            generator class="uuid.hex" /
        /id
        many-to-one name="certificate"
        class="edu.dgut.ke.model.Certificate"
        unique="true"
        column="cardId"
        cascade="all"
       
        /many-to-one
        many-to-one name="team" class="edu.dgut.ke.model.Team"
            column name="TEAMID" length="32" not-null="true" /
        /many-to-one
        property name="studentname" type="java.lang.String"
            column name="STUDENTNAME" length="16" not-null="true" unique="true" /
        /property
    /class
/hibernate-mapping
注意：对one-to-one 关系进行延迟加载和其他关系相比稍微有些不同。many-to-one 的延迟加载是在配置文件的class 标签
上设置 lazy="true" ，one-to-many 和 many-to-many 的延迟加载是在 set 标签中设置lazy="true"。而one-to-one 不只要在 classs
标签设置 lazy="true"，而且要在one-to-one 标签中设置constrained="true" 。
如果不设置constrained="true"，则一对一查询使用默认的预先抓取策略(fetch="join")。